Final answer:
An elderly couple with a fixed income at 150% of the U.S. poverty threshold is least likely to suffer from food insecurity because they are part of demographic groups with lower poverty rates compared to single-parent, African American households.
Step-by-step explanation:
To determine which family is least likely to suffer from food insecurity in the United States, it's important to consider factors such as race, household composition, and income in relation to the poverty threshold. Based on data from the U.S. poverty line, poverty rates are lower for whites, the well-educated, and elderly people, especially those with incomes above the poverty line.
Therefore, an elderly couple with a fixed income at 150% of the U.S. poverty threshold is less likely to experience food insecurity compared to a single African American mother of a high-school student, since African Americans, single-parent households, and particularly households headed by females tend to have much higher poverty rates.